Focus on Core Issues to Control Blackgrass

Focus on Core Issues to Control Blackgrass20 September 2016

Focusing on the conditions that favour blackgrass development could go a long way to helping control the problem on UK farms, says ProCam’s technical director Dr Tudor Dawkins. With just about every crop in the rotation on farms right across the main arable areas of England currently affected, addressing the issue at a grass roots level is now essential, he believes.

“The truth is chemistry is not coping well in some areas of the country and the non-chemical approaches to containing blackgrass do not necessarily suit all farming systems and often carry significant financial implications. But with blackgrass being one of the biggest limiting factors to crop yields, we have to get back to why the weed is such a problem in the first place. Blackgrass is favoured by wet soil conditions so the first port of call for many growers should be assessing drainage”

“It’s imperative that drains function properly so water can be carried away from the field. It’s not uncommon to find conduits under field entrances and ditches completely blocked.In addition, drain outfalls may be below the bottom of ditches so these need to be completely cleared so water can flow freely away from the field.”

Another problem is that compacted layers within the soil profile often prevent water percolating down the soil profile to the drains, he says.

“Dig pits and check for areas of soil compaction in the profile. If you find compact layers, remove them by working with tines and/or discs working just below the impeding layers to fully disrupt them. It’s worth considering mole ploughing on soils where it is suitable to do so. Moles can last for several years on heavier soils and play a key role in removing standing water over winter.”

Cultivation techniques and seedbed preparation also need reappraising, he says.

“A well set plough which fully inverts the soil will effectively bury seed which should remain buried for at least 2-3 years but this is only effective if the seed is not already uniformly distributed through the soil. ProCam studies have shown that blackgrass can emerge from as deep as 10 cm, he explains. One plant emerging from depth, out of the influence of residual herbicides, can produce up to 36 tillers with 100-200 seeds per head so this can completely undo the benefit of ploughing. Furthermore, if the land is ploughed again too soon, viable seed is returned to the surface layers where it germinates and perpetuates the problem.”

Where land is ploughed, good seedbed preparation and a robust herbicide programme will still be needed”, adds Dr. Dawkins.

“Currently, our effective grass weed chemistry relies heavily on soil acting, residual products, which need to be applied pre and very early post-emergence of crop and weed. These products work best in fine, consolidated seedbeds and when soils are moist and cool so they can be more effectively picked up by the emerging weeds”.

“Cooler soils slow herbicide degradation and keeps them active longer through the main germination period of the grass weeds. In autumn 2015, however, soil temperatures remained stubbornly high well into the winter period so herbicide performance was greatly diminished.”

Delaying drilling can play a large part in helping residual herbicides deliver their optimum efficacy as well as allowing more time to tackle the problem after harvest, he points out.

“Delaying sowing into October is a must where blackgrass populations are high as up to 80% of blackgrass seed germinates in September and October. Later sowing allows more time to remove a ‘flush’ of blackgrass with glyphosate and soil conditions are more likely to suit the herbicides’ mode of action.”

But delayed drilling can carry risks, particularly on heavier land, he says.

“If the weather closes in, opportunities for late drilling on heavier soils can be limited so you need to prepare as good a seedbed as possible so that when a drilling window does appear you can get on and get the job done.”

The bottom line is we need to start thinking about blackgrass differently, Dr. Dawkins concludes.

“A lot can be achieved in the future through focusing on basic management as not only can this have a profound effect on weed numbers in itself, it also makes available chemistry more effective.”